1. Field of the Invention
The present invention relates generally to a vibration damping actuator for use as an active vibration damping apparatus and to an active vibration damping apparatus employing the same, and particularly to a vibration damping actuator suitable for use in a vibration damping apparatus such as an automobile engine mount, body mount, damper, or the like, and to an active vibration damping apparatus employing the same.
2. Description of the Related Art
In order to reduce vibration in an automobile body or other component that is very expected to be vibration-damped, there have been employed vibration damping devices that typically utilize vibration attenuating means, such as a shock absorber or rubber elastic body, or alternatively vibration isolating means that utilize the spring action of a coil spring, rubber elastic body, or the like. However, all of these vibration damping devices exhibit only passive damping action, resulting in the problem of an inability to exhibit adequate damping action in instances where, for example, the vibration to be damped has a characteristics such as frequency, that varies; or in cases where advanced vibration damping is required. Accordingly, in recent years, there have been developed and researched a number of active vibration damping devices that actively and in an offsetting manner reduce vibration to be damped, by means of exerting oscillating force on the component to be damped or the vibration damping device. Examples include those disclosed in Citations 1–4 listed hereinbelow.
In such active vibration damping devices, an actuator is needed in order to generate oscillating force, and the actuator needs to have highly controllable frequency and phase as regards the oscillating force generated thereby. A vibration damping actuator appropriate for use in an active vibration damping device may employ a coil, controlling electromagnetic force or magnetic force generated by means of controlling current flow to the coil.
More specifically, as taught inter alia in Citations 1–4, a suitable design for such a vibration damping actuator typically has a guide hole extending on the center axis of a cup-shaped housing; an output member disposed spaced apart from the opening end of the housing, with the output member connected to the housing by an elastic connecting rubber part, and a guide rod disposed on the output member inserted into a guide hole; a coil member provided to either the housing or the output member; and an armature including a ferromagnetic body and/or permanent magnet disposed on the remaining housing or output member. By supplying electrical current through the coil, oscillating force is exerted on the output member by the armature, causing the output member to undergo oscillating displacement in the center axial direction of the housing, on the basis of the guiding action of the guide rod by the guide hole.
In order to actuate vibration of an output member in a high frequency range of several tens of Hz or greater, it is appropriate to employ a guide mechanism for guiding the output member in the actuation direction, and to ensure that the gap between the opposed faces of the coil member and the armature has size that is small and controlled with a high degree of accuracy.
However, where a guide rod guide mechanism relying on a guide hole, and a tiny gap structure for the output portion is employed, components on both the output member side and the housing side should be assembled with a high degree of accuracy. Therefore, when assembling the housing equipped with either the coil member or armature, and the output member affixed to the remaining coil member or armature by inserting the guide rod of the output member into the housing in the axial direction, it is necessary to take extreme care in positioning of the members in a direction perpendicular to an axis direction of the housing (hereinafter refereed to as the “axis-perpendicular direction”), leading to a tendency of increasing difficulty in assembling operation. Even after assembly, a high degree of accuracy in relative positioning of the housing and output member (guide rod, etc.) is also required in order to efficiently obtain consistent output characteristics, which has the problem of being difficult to achieve.
[Citation 1]                JP-A-9-49541        
[Citation 2]                JP-A-9-89040        
[Citation 3]                JP-A-10-231886        
[Citation 4]                JP-A-2001-1765        